Ingredients for Life: Carbon

Teacher Resource

Posted 10.21.05

NOVA

Carbon is the basis of all organic molecules. It is also one of the most abundant elements in the universe. This video segment adapted from NOVA illustrates the special characteristics of carbon that make it an essential ingredient for life.

Background

The structure of the carbon atom allows for chemical bonding with up to four other atoms, which makes possible the vast array of chemical arrangements in organic molecules. All life on Earth depends on organic molecules, the primary components of which are also some of the most abundant elements in the universe: carbon, hydrogen, nitrogen, oxygen, sulfur, and phosphorus.

Naturally occurring elements are produced in the cores of stars by a process known as nucleosynthesis. Just after the Big Bang, when the universe was very young, the only elements present were hydrogen, helium, and a trace amount of lithium. As stars formed and nuclear fusion ignited within their cores, other elements were created. These elements are all lighter than iron, and include carbon, oxygen, and nitrogen. As low-mass stars neared the ends of their lives, they lost their outer layers into space where the material became the interstellar medium -- the gas and dust between stars. Before the outer layers were expelled, convection enriched them by "dredging up" chemical elements from stellar interiors. It is thought that the majority of the carbon in the universe comes from this phase of stellar evolution. Elements heavier than iron were created in the much more dramatic endings of high-mass stars. The cataclysmic explosions of these supernovae created the intense conditions needed to form the heaviest elements, which were then also dispersed into the interstellar medium.

The interstellar medium is recycled to form new stars and planets. And because the relative abundances of the elements are the same throughout the universe, all planets, moons, asteroids, and comets should have the same basic ingredients available to them. In fact, observations of other stars and galaxies have shown similar chemical abundances: 98% of the mass is hydrogen and helium, and all other elements compose the remaining 2%. That 2% may not seem like much, but it is enough to create all living things on Earth. One of the most common of the remaining elements is carbon -- and organic molecules have even been observed in interstellar clouds and found in comets and meteorites.

While it is still not clear how life on Earth originated from basic organic molecules, the fact is that life exists. If basic organic molecules were able to create life on Earth, and they are available elsewhere in the universe, it is not unreasonable to wonder if life has also developed elsewhere.